1. Field of the Invention
This invention relates to equipment useful in high frequency radio communications systems. More particularly, the invention is concerned with a switchable polarizer for changing the polarization of signals passing through a waveguide.
2. Description of Related Art
Rotator elements placed in-line with a waveguide are useful for changing the polarization of a signal prior to further processing. For example, waveguides associated with antennas often incorporate switchable polarizer functionality to allow conversion of the antenna between horizontal and vertical polarization.
The geometries of standard in-line polarizer transition elements are well known in the art. Prior switchable polarizer solutions have typically incorporated one of three general approaches. First, the polarizer element may be removable. A user alternatively installs one or another dedicated component by fully disassembling the waveguide and inserting a separate transition element designated for each desired polarization. Where no transition is required, the polarizer element is typically a straight pass through waveguide section to minimize electrical losses. This approach requires the inventory and storage, perhaps for years, of redundant transition components until they are needed, if ever.
Second, the transition components may be formed as a plurality of plates that bolt together in alternative configurations for each desired polarization. Further developments of this approach have used pins and slots to allow rotation of the various plates between polarization configurations without requiring complete removal and restacking of the plurality of plates. However, each of the transitions between the separate plates inhibits electrical signal flow, creating an electrical loss and contributing to an overall tolerance error that increases with the number of separate components. High manufacturing tolerances required to minimize these effects significantly contributes to the cost of this solution. Further, the plurality of plates increases the length of the resulting assembly, increasing overall structural requirements. When no polarization change is required, the plates are adaptable into a stacked straight pass through waveguide section configuration.
A third solution is to form a single transition component having transition cavities and faces formed complementary to dual orthogonal polarizations depending upon the connection orientation of the associated waveguides. This solution reduces the number of overall components required and thereby the associated transition errors and or tolerance losses related to the prior multiple separate components. However, where no signal change is desired, rather than allowing the signal to pass through without transition, this solution performs a signal translation having a net effect of zero degrees. Therefore, this solution forces a compromise wherein a significant electrical loss is incorporated by the transition element whether or not a polarization change is desired. Further, the orientation of associated transmitter or receiver equipment may be fixed, for example for environmental sealing and or cooling purposes, preventing their rotation with respect to a waveguide mounting point.
Depending upon the specific equipment combination used, a waveguide cross-section transition between, for example, a circular to rectangular waveguide may also be required as a further additional component located for example, between an antenna and a transmitter or receiver.
Competition within the waveguide and RF equipment industries has focused attention upon improving electrical performance, reduction of the number of overall unique components, as well as reductions of manufacturing, installation and or configuration costs.
Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art.